Hodgins: (about the victim's severed head) So... not a zombie?
Cam: Zombies have to be beheaded or they eat your brains.
Brennan: There are no such things as zombies or vampires or ghosts.
Oliver: The first law of thermodynamics states that energy is neither created nor destroyed. So when we die, all that energy has to go somewhere, right? I believe that if we die with an abundance of this power, it can become forever imprinted on the immediate environment.
Hodgins: And that imprint, that's our ghost?
Hodgins: (admiring) Can we keep him?
Brennan: I haven't decided yet.